Bidirectional Glenn procedure improves the mechanical efficiency of a total cavopulmonary connection in high-risk fontan candidates

Background - A total cavopulmonary connection (TCPC) is a widely performed surgical procedure for Fontan candidates. High-risk candidates who have undergone the bidirectional Glenn procedure (BDG) before TCPC have shown good results. The exact mechanism of this procedure, however, is still poorly understood. We hypothesized that a volume reduction with BDG improved ventricular contractility, thereby optimizing mechanical efficiency after TCPC. Methods and Results - We measured percent normal systemic ventricular end-diastolic volume (%N-EDV), contractility (end-systolic elastance; E_es), afterload (effective arterial elastance; E_a), and mechanical efficiency (ventriculoarterial coupling; E_a/E_es) on the basis of the cardiac catheterization data before and after TCPC. Eighteen patients who underwent staged TCPC after BDG (staged group) were compared with 29 patients who underwent primary TCPC (primary group). E_es and E_a were approximated as follows: E_es=mean arterial pressure/minimal ventricular volume, and E_a=maximal ventricular pressure/(maximal ventricular volume-minimal ventricular volume), and E_a/E_es was then calculated. The ventricular volume was normalized with the body surface area. A canine experimental model with conductance catheter was used to validate the accuracy of this approximation of E_es and E_a. %N-EDV decreased after TCPC in both groups. In the staged group, a smaller ventricular volume resulted in better contractility (E_es. Although afterload (E_a) increased in both groups, the increment of E_a was smaller in the staged group. These changes resulted in an improvement of E_a/E_es in the staged group, whereas E_a/E_es increased in the primary group. Conclusions - The volume reduction of BDG preceding TCPC allows for any afterload mismatch to be corrected, thereby improving ventricular energetics after TCPC.